1. Field of the Invention
The present invention generally relates to a mobile terminal apparatus such as a mobile telephone equipped with a cap formed at a part of a housing for an opening for a connector, earphone jack, memory card slot, etc., and more particularly, to a mobile terminal apparatus with a balance between an insertion force for easy attachment of a removable cap into the housing and a withdrawal resistance for preventing the cap from easily slipping off.
2. Description of the Related Art
In recent years, various types of mobile terminals are on the market, such as a small-size information processing terminal including a mobile telephone and a personal digital assistant (PDA), a small-size music player, and a portable television. The mobile terminals are equipped with a connector for connecting an external device for data communication, power supply, etc., as well as an earphone jack, memory card, etc., depending on the applications. The connector is disposed in an opening formed at a part of a housing and exposed to outside. To hide the connector and other connecting means not in use for protecting them from water and dust and for the aesthetic point, a cap is attached to the housing for the opening in such a manner that the cap can be removed when the connector and other connecting means are used (see, for example, Japanese Patent Application-Laid-Open No. 2005-44547).
A first type of cap uses a claw structure. FIG. 5 is a perspective view of a conventional claw structure before being attached, and FIG. 6 is a partial cross-section of the conventional claw structure after being attached. The claw structure includes a claw 101 and a claw engaging rib 113. The claw 101 is made of a flexible material and formed as a part of a cap 100, while the claw engaging rib 113 is provided in a housing 110 of a two-split structure made of housings 110 and 111. The housing 110 includes an engaging gap 112 that is narrower than the claw 101 to prevent the claw 101 from slipping off from the claw engaging rib 113 once the cap 100 is attached. For attaching the cap 100, the claw 101 is inserted through a recess 116 formed at a part of the housing 111 into an opening 115 that is formed between the housings 110 and 111 for accommodating a connector 114 installed in the housing 111, toward the claw engaging rib 113. In the engaging gap 112, projections of the cap 100 and/or the housing 110 are resiliently deformed to force the claw 101 to engage the claw engaging rib 113. For facilitating the insertion operation during attachment, inclined planes 102 and/or 117 are provided in the claw 101 and/or the claw engaging rib 113.
A second type of cap uses a rotary attachment structure. FIG. 7 is a perspective view of a conventional rotary structure before being attached; FIG. 8 is a bottom view of a cap during attachment; and FIG. 9 is a perspective view of the attached cap. The rotary attachment structure includes a slit 122 in a housing 120 of a two-split structure composed of housings 120 and 121, formed in a direction orthogonal to the opening/closing direction of a cap 130, and a fixing protrusion 131 formed at the cap 130, with a shape and dimensions adapted to the slit 122, in the same direction as the extracting direction. As shown in FIG. 8, the cap 130 is first placed at an angle orthogonal to the attachment direction to the engage the fixing protrusion 131 in the slit 122, and then rotated in the direction indicated by the arrow until it is positioned in place and finally attached as shown in FIG. 9. In some cases, protrusions 123 are provided inside the housing 120 around the slit 122, which engage the fixing protrusion 131 of the cap 130 to prevent the cap 130 from rotating in the disengaging direction. Another similar structure has a slit formed at the cap, and a fixing protrusion formed in the housing. An attachment structure similar to the second type is disclosed in Japanese Patent Application-Laid-Open No. 2002-9911.
A third type of cap uses a fixing structure using a pin or the like. FIG. 10 is a perspective view of a conventional pin fixing structure before being attached. The pin fixing structure includes a hole 142 formed in an attachment part 141 of a cap 140, and a fixing pin 151 formed inside a housing 150 of a two-split structure. The cap 140 is attached and fixed to the housing 150 by engaging the fixing pin 151 in the hole 142 of the cap 140 before the apparatus is completely assembled.
According to the convention technology, efforts have been made by selectively using a suitable structure among the first to third types described above, based on a priority of requirements including the structure of a housing, easiness of design, cost, and repairability. However, none of the above structures has satisfied all of the requirements such as a smaller and thinner cap attachment portion, which is essential for a smaller and thinner apparatus, a high withdrawal resistance preventing the cap from easily slipping off during cap opening/closing operation, a low insertion force for easy assembly, complete or substantially complete insusceptibility to variations in part and assembly precisions, excellent maintainability requiring no special tools or disassembly of the apparatus, and prevention of damages that may be caused by an abnormally strong extraction force.
In the first type, for example, the withdrawal resistance depends on the engaging amount of the claw 101 to the claw engaging rib 113. To increase the withdrawal resistance, the engaging amount should be increased or the material of the claw 101 hardened. If the engaging amount is increased or the material of the claw 101 is hardened, however, more insertion force is required, which adversely affects the easiness of assembly and repairability, because projections of the cap 100 and/or the housing 110 must be resiliently deformed for forcing the claw 101 to pass over the claw engaging rib 113 through the engaging gap 112 that is narrower than the claw 101. On the other hand, if the engaging amount or material hardness of the claw 101 is decreased for reducing the insertion force, the withdrawal resistance is reduced, which may cause the cap 100 to slip off and be lost. In the first type, the withdrawal resistance and the insertion force are so closely related with each other as described above, it is difficult to achieve both a high withdrawal resistance and a low insertion force.
In particular, in a structure in which the engaging gap 112 is formed between the upper end of the claw engaging rib 113 and a plurality of component members facing this upper end, including a circuit board 118, the connector 114, and a sheet member 119 as shown in FIG. 6, the engaging gap 112 is easily affected by variations of individual component and assembly precisions. Accordingly, it is difficult to keep a precise engaging amount of the claw 101 of the cap 100 to the claw engaging rib 113 of the housing 110 to secure a stable withdrawal resistance and insertion force. A strict control of dimensional tolerances of components and assembly variations during design and manufacturing stages will incur not only additional control cost and thus increased total cost, but also additional development steps of a mobile terminal equipped with such a cap, for regulating and controlling the balance between the withdrawal resistance and the insertion force and repeatedly adjusting the dimensions and shapes using prototypes or actual models.
On the other hand, the second type can easily secure a high withdrawal resistance and a low insertion force, since the withdrawal resistance and the insertion force are not related to each other. An attachment 132 of the cap 130, however, limits the degree of freedom in design, since it is visibly disposed on the outer surface of the housing 120 as shown in FIG. 9 for example. Its rotary attachment structure also limits the shape of the externally visible part of the attachment 132 and thus the degree of freedom in designing the shape of the attachment 132. Furthermore, a total thickness of the area where the attachment 132 is disposed must accommodate the thickness of the cap 130, that of the housing 120, and that of the fixing portion of the cap 130, which makes difficult a smaller and thinner design. It also requires two different operations of insertion and rotation for attachment, resulting in increased attachment steps.
The third type provides secure attachment of the cap 140 to the housing 150, as well as a high withdrawal resistance, since the hole 142 formed in the attachment part 141 of the cap 140 fits into the fixing pin 151 in the housing 150. The easiness of assembly and maintainability is reduced, however, because the hole 142 must be fitted onto the fixing pin 151 before the two-split housing is assembled. If an abnormally strong extraction force is applied to the cap 140, the hole 142 does not disengage from the fixing pin 151 and the attachment part 141 of the cap 140 and/or the fixing pin 151 of the housing 150 may be damaged.